Just beat the game, so don't highlight my spoilers unless you have too!
(SPOILER)I spared Darko, but went after Dimitri. Apparently Roman dies instead of Kate if you deal with him instead. The difference between Darko and Dimitri was that Darko was nothing, just a stain. Dimitri, that smurfer was still going around hurting people without regrets, he just had to go. Last mission was smurfing cool with the motorbike jump onto the helicopter! Disappointed Packie wasn't with us though, I'd have thought he would have wanted revenge for his sister. Oh well.
As for the other kill choices, I iced Playboy. Mostly because Dan told me to, but eh, even if he hadn't I would've done so anyway, 'cause Niko seemed to like Dwayne. As for Francis vs Derrick, I went with killing Derrick. Francis was slime, but Derrick was going to rat him out. Snitches get stitches!
This game genuinely made me stop and think about my choices. It was incredibly powerful. I mean sure, the gameplay is world class, we all know that, but wow, the story was fantastic too, and I actually ended up caring about Niko and Roman.